1. Field of the Invention
The present invention relates to an optical device for optical communication using an optical fiber as a transmission medium, and particularly to a mechanism for connecting the optical fiber to an optical unit by using a ferrule.
2. Description of the Related Art
As an optical device used in an optical communication, an optical module comprising an optical fiber connected to an optical unit by using a ferrule is used in various applications. FIG. 1 is an enlarged sectional view showing a conventional example of a connection portion of an optical fiber in an optical module provided with a ferrule. In the specification, for the sake of ease of description, the right side of each of FIGS. 1 to 7D represents the front side of the optical device, and the left side represents the rear side of the optical device.
Referring to FIG. 1, an optical fiber 1 is inserted into a ferrule 3a provided at the front of an optical unit section (not shown in FIG. 1) from the front side, and fixed to the optical unit section. This structure will be described in detail below.
The optical fiber 1 has a structure in which a glass portion 1a comprising a clad and a core is coated with a UV resin layer 1b, and further coated with a coating layer 1c of a nylon or elastomer material.
The glass portion 1a of the optical fiber 1 is exposed in the vicinity of the rear end (the left side of the drawing), and the rear end of the glass portion 1a is press-fitted into a capillary 3a-2 made of zirconia. The rear end surface of the capillary 3a-2 is polished together with the glass portion 1a of the optical fiber 1. The optical fiber 1 and the capillary 3a-2 are covered with a metal blank 3a-1, and the optical fiber 1 is further fixed to the blank 3a-1 at the fixing joint portion 2 with an adhesive composed of an epoxy resin or the like. The capillary 3a-2 into which the optical fiber 1 is press-fitted, and the blank 3a-i are fixed to the front side of a case (not shown in FIG. 1) in which an optical part is contained. The capillary 3a-2 and the blank 3a-1 is formed as the ferrule, which constitutes a part of the optical unit section.
As described above, in the conventional optical device, the optical fiber serving as a transmission medium is fixed to the optical unit section, for exsample to the blank 3a-1, with an adhesive or the like. In such an optical device in which the optical fiber 1 is fixed and connected, the outer peripheries of the ferrule and the optical fiber 1 which is exposed from the front of the ferrule are covered with a flexible tube 5 (cap) made of a flexible material such as rubber or elastomer. In this structure, the bend radius of the optical fiber 1 is increased as much as possible to decrease the bending stress exerted on the optical fiber 1, suppressing breakage of the optical fiber 1.
However, the conventional optical device comprising the flexible tube 5 for covering may cause breakage of the optical fiber 1 during the work of installing the optical fiber 1 to the optical device. The problem of breakage cannot be easily solved even by the method of disposing a protecting member made from an elastic member (specifically, a coil spring) in the flexible tube 5 because the fiber breaking load (breakage resistance) is not changed.